Messing with Kirby's lunch or his nap is equal killing John Wick's dog, you don't expect to walk out alive after that.

Kirby literally has infinite power, confirmed by both the director of modern Kirby games and in one of the descriptions for Planet Robobot.

The only reason why he doesn't near instantly destroy all of the enemies in the series is because he's a child, unaware of his true capability.